Blowers and rotary compressors



Aug. 11, 1964 E. w. RUNDLE BLOWERS AND ROTARY COMPRESSORS 2 Sheets-Sheet1 Filed May 7, 1962 x m wwwwww y u 9 www g w /H v w -m ,mW mu -ww -mw b[W -w -m xmmwmww www Home Aug. 11, 1964 E. w. RUNDLE 3,144,201

BLOWERS AND ROTARY COMPRESSORS Filed May 7, 1962 2 Sheets-Sheet 2 y 3)MM W United States Patent 3,144,201 BLOWERS AND ROTARY COMPRESSORS EricWilliam Rundle, Leatherhead, England, assignor to Plannair Limited,Surrey, England, a British company Filed May 7, 1962, Ser. No. 193,369Claims priority, application Great Britain May 9, 1961 2 Claims. (Cl.230120) This invention relates to blowers and rotary compressors, and isparticularly concerned with bladed rotors or impellers for use in suchmachines.

A common fault among axial-flow blowers and other bladed machines isthat they tend to stall at a particular rate of volumetric flow and at aparticular delivery pressure-the actual point of stall being dependenton the specific construction of the machine. This necessarily restrictsthe range of delivery pressures and rates of flow over which the machinewill operate satisfactorily.

In many instances this restriction of the operating range is not asevere handicap, but in certain cases it is highly desirable or evenessential to use a blower which cannot stall. For example, it isfrequently necessary to provide an air filter on the inlet side of ablower, with the result that the resistance to air-flow increases as thefilter becomes dirty. A condition is often reached in such installationswhere the pressure drop across the filter is greater than the maximumpressure rise within the blower, which leads to stalling of the blowerand a drastic reduction in the air delivered from it. Similarly, theblower or blowers of an aircraft ventilation system should not stall ifall the discharge ports into the passenger cabin are closed.

The present invention has been devised to meet this requirement for anon-stall blower or compressor, and according to the invention a rotoror impeller for use in such machines comprises a number of rotor bladeseach having flow-surfaces on both sides of the blade which curve in onedirection from the leading edge of the blade to a point or line morethan half-way towards its trailing edge and which then curve in anopposite direction over the part of the blade adjacent the trailingedge.

The theory behind the invention and a number of other features which canbe included in the rotor or impeller will now be explained withreference to the particular example illustrated in the accompanyingdrawings, in which:

FIGURE 1 is a graph showing the pressure/flow operating range of atypical axial-flow blower in general use at the present time;

FIGURE 2 is a similar graph showing the pressure/ flow operating rangeof a blower in accordance with the invention;

FIGURE 3 is a rear end view of a rotor or impeller in accordance withthe invention;

FIGURE 4 is a side view of the rotor shown in FIG- UREflB;

FIGURE 5 is a front end view of the rotor shown in FIGURE 33;

FIGURE 6 is a diagram showing the cross-section of one of the rotorblades at its root, its tip, and its midheight; and

FIGURE 7 is a vertical section through a typical axialflow blowerincorporating the invention.

As indicated above, FIGURE 1 illustrates the operating characteristicsof a typical axial-flow blower in general use at the present time, theordinate X representing the pressure rise within the blower expressed asa percentage and the ordinate Y representing the volume flow through theblower, also expressed as a percentage. It will be seen from inspectionof this figure that the blower has an operating range between the pointsC and D on the line B which is restricted at one end by a so-calledbreakdown point B of pressure and flow which causes 3,144,201 PatentedAug. 11, 1964 the blower to stall as shown by the broken line A. This isnot a serious disadvantage in many installations where blowers orcompressors are used, but in certain instances it is most undesirablethat the blower should stall once the delivery pressure and rate ofvolumetric flow reach a certain point.

It is accordingly an aim of the present invention to produce a blower orcompressor which has an operating range such as that shown by the line Fin FIGURE 2, that is to say, an operating range which is not restrictedby the breakdown point E of FIGURE 1.

We have found that a machine which meets this requirement can beprovided if the rotor or impeller blades are shaped in a particularmanner so as to create a flowpattern through the machine which does notgive rise to conditions of stall. FIGURES 3 to 6 show a rotor orimpeller ltl having airfoil-section blades 12 shaped in this manner, andit will be noted that the main characteristic of the blades is that theflow-surfaces 14 and 16 adjacent their trailing edges 18 curve in anopposite direction to those parts of the flow-surfaces 14 and 16 whichare adjacent the leading edges 20 of the blades, the flow surfaces 14and 16 being at the same time so disposed that no portion of themproduces axial or near-axial flow of the air. It is found that blades ofthis construction produce a stable air flow at their trailing edges overthe whole pressure/flow range of the blower, which is in marked contrastto the unstable air flow which occurs at particular pressures and ratesof flow in blowers having rotor blades of conventional design.

FIGURE 6 shows three cross-sectional views of one of the blades, thefirst cross-section 22 being taken at the root of the blade, the secondcross-section 24 being taken at the mid-height of the blade, and thethird cross-section 26 being taken at the tip of the blade. It will beseen that the reverse curvature of the flow-surfaces adjacent thetrailing edge of the blade is substantially constant at all heights ofthe blade, and that the flow-surfaces at the trailing edge are so formedas to throw the air off the blade in a direction which is approximatelyradial to the axis of the rotor 10.

The actual rotor or impeller shown in the drawings has eight rotorblades, although the number of blades provided is not critical, and itwill be seen that the blades overlap each other to a certain extent whenthe rotor is viewed along its axis. The result is that the width of thegap between adjacent blades measured at right angles to the direction offluid flow between them is less at the leading edge of one of the bladesand at the trailing edge of the other blade than in the central portionof the gap, the best results being obtained when adjacent blades overlapeach other by between 15 and 40% of their area when viewed along theaxis of the rotor. This ensures that the air is compressed, expanded andthen re-compressed as it passes between adjacent blades. Further, it isdesirable that the trailing edge 18 of each blade should lie parallel toits leading edge 20, although this does not appear to be a criticalrequirement as satisfactory results can still be obtained if the leadingedge and the trailing edge are out of parallel by as much as 15".

The reverse curvature adjacent the trailing edge 18 of the blades 12shown in the drawings occurs only over the last quarter of theflow-surfaces 14 and 16. However, in some instances it may be desirablefor the reverse curvature to commence directly after the half-wayposition between the leading and the trailing edges of the blades. Inboth cases the thickness of the blades along their portions of reversecurvature is no greater at any point than the thickness of the blades atthe transition point where the reverse curvature commences.

The invention is applicable to many different kinds of blade, but it hasbeen found particularly advantageous when applied to a rotor bladeconstructed in accordance with the invention described in British PatentNo. 751,954. The rotors or impellers can be manufactured in one piece bya casting, injection moulding or milling operation, and may be made ofaluminium-alloy, stainless steel, synthetic plastic and other materials.

it has been found that blowers or compressors in accordance with theinvention give improved results if the incoming air or other fluidimpinges upon the leading edges of the rotor blades in an axialdirection, that is to say, a direction lying parallel to the axis of therotor. This can be ensured by arranging a honeycomb grille on the inletside of themachine, the grille thereby serving to counteract anytendency of the incoming air to flow in a non-axial direction. Anaxial-flow blower of this construction is shown in FIGURE 7 where agrille 28 is arranged on the inlet side of the cylindrical casing 30 ofthe machine. The rotor 10 is fastened to the shaft 36 of a driving motor38 arranged in a motor-housing 34, and in this instance a secondhoneycomb grille 32 is also fitted on the delivery side of the bloweraround the motorhousing 34. The stator blades of the blower are shown at40, so that it will be seen that the stator blades are arrangeddownstream of the rotor blades 12 in the direction of fluid-flow and areseparate from the rotor blades.

The invention has been described above primarily in connection withsingle-stage blowers or compressors, but it is also applicable tomulti-stage machines.

I claim:

1. A rotary compressor comprising an axial flow rotor having a centralhub, driving means drivingly connected to said hub, a plurality ofradially-extending rotor blades peripherally spaced about said hub so asto overlap each other to a substantial extent and having their innerends extending from said hub, a plurality of stator blades, separatefrom said rotor blades, arranged downstream of said rotor blades in thedirection of fluid flow, a curved forward flow-surface and a curved rearflow-surface on each of said rotor blades, and flow-surfaces beingcurved in one direction from the leading edge of each of said rotorblades to a transition point at least half-way towards the trailing edgeof each of said blades, and being curved in an opposite direction tosaid first-mentioned direction over the part of each rotor bladeadjacent said trailing edge, said blades being fixed relatively to eachother on said hub so that the width of the gap between adjacent rotorblades measured at right angles to the direction of fluid flowtherebetween is less at the leading edge of one of said blades and atthe trailing edge of the other of said blades than in the centralportion of said gap, whereby fluid flowing through said gap iscompressed, expanded and then re-compressed by said adjacent rotorblades, and flow-surfaces on said rotor blades being at a substantialangle to the rotational axis of said rotor at all points between saidleading edges and said trailing edges of said rotor blades, thethickness of said rotor blades along their opposite-curved portionsadjacent their trailing edges being no greater at any point than thethickness of said blades at said transition point on each rotor blade;the adjacent rotor blades overlapping each other by between 15 and 40%of their area as viewed along the rotational axis of said rotor; and ahoneycomb flow-guiding grille having only axially extending flowpassages on the inlet side of said compressor immediately adjacent theleading edges of the rotor blades to guide the incoming fluid in anaxial direction and to counteract any tendency of the incoming air toflow in a non-axial direction.

2. A rotary compressor according to claim 1, in which the portions ofsaid flow-surfaces adjacent the trailing edges of said rotor blades formtrailing surfaces directed to throw fluid off said blades in a directionwhich is approximately radial to the rotational axis of said rotor.

References Cited in the file of this patent UNITED STATES PATENTS1,448,393 Eastman Mar. 13, 1923 2,161,027 Dollinger June 6, 19392,260,169 Couch Oct. 21, 1941 2,784,551 Karlby et al. Mar. 12, 19572,931,563 Eggleton Apr. 5, 1960 2,935,246 Roy May 3, 1960 FOREIGNPATENTS 444,206 Great Britain Mar. 17, 1936' 747,750 France Apr. 4, 1933847,018 France June 19, 1939 937,969 Germany Jan. 19, 1956 955,377Germany Jan. 3, 1957

1. A ROTARY COMPRESSOR COMPRISING AN AXIAL FLOW ROTOR HAVING A CENTRALHUB, DRIVING MEANS DRIVINGLY CONNECTED TO SAID HUB, A PLURALITY OFRADIALLY-EXTENDING ROTOR BLADES PERIPHERALLY SPACED ABOUT SAID HUB SO ASTO OVERLAP EACH OTHER TO A SUBSTANTIAL EXTENT AND HAVING THEIR INNERENDS EXTENDING FROM SAID HUB, A PLURALITY OF STATOR BLADES, SEPARATEFROM SAID ROTOR BLADES, ARRANGED DOWNSTREAM OF SAID ROTOR BLADES IN THEDIRECTION OF FLUID FLOW, A CURVED FORWARD FLOW-SURFACE AND A CURVED REARFLOW-SURFACE ON EACH OF SAID ROTOR BLADES, AND FLOW-SURFACES BEINGCURVED IN ONE DIRECTION FROM THE LEADING EDGE OF EACH OF SAID ROTORBLADES TO A TRANSITION POINT AT LEAST HALF-WAY TOWARDS THE TRAILING EDGEOF EACH OF SAID BLADES, AND BEING CURVED IN AN OPPOSITE DIRECTION TOSAID FIRST-MENTIONED DIRECTION OVER THE PART OF EACH ROTOR BLADEADJACENT SAID TRAILING EDGE, SAID BLADES BEING FIXED RELATIVELY TO EACHOTHER ON SAID HUB SO THAT THE WIDTH OF THE GAP BETWEEN ADJACENT ROTORBLADES MEASURED AT RIGHT ANGLES TO THE DIRECTION OF FLUID FLOWTHEREBETWEEN IS LESS AT THE LEADING EDGE OF ONE OF SAID BLADES AND ATTHE TRAILING EDGE OF THE OTHER OF SAID BLADES THAN IN THE CENTRALPORTION OF SAID GAP, WHEREBY FLUID FLOWING THROUGH SAID GAP ISCOMPRESSED, EXPANDED AND THEN RE-COMPRESSED BY SAID ADJACENT ROTORBLADES, AND FLOW-SURFACES ON SAID ROTOR BLADES BEING AT A SUBSTANTIALANGLE TO THE ROTATIONAL AXIS OF SAID ROTOR AT ALL POINTS BETWEEN SAIDLEADING EDGES AND SAID TRAILING EDGES OF SAID ROTOR BLADES, THETHICKNESS OF SAID ROTOR BLADES ALONG THEIR OPPOSITE-CURVED PORTIONSADJACENT THEIR TRAILING EDGES BEING NO GREATER AT ANY POINT THAN THETHICKNESS OF SAID BLADES AT SAID TRANSITION POINT ON EACH ROTOR BLADE;THE ADJACENT ROTOR BLADES OVERLAPPING EACH OTHER BY BETWEEN 15 AND 40%OF THEIR AREA AS VIEWED ALONG THE ROTATIONAL AXIS OF SAID ROTOR; AND AHONEYCOMB FLOW-GUIDING GRILLE HAVING ONLY AXIALLY EXTENDING FLOWPASSAGES ON THE INLET SIDE OF SAID COMPRESSOR IMMEDIATELY ADJACENT THELEADING EDGES OF THE ROTOR BLADES TO GUIDE THE INCOMING FLUID IN ANAXIAL DIRECTION AND TO COUNTERACT ANY TENDENCY OF THE INCOMING AIR TOFLOW IN A NON-AXIAL DIRECTION.